The invention relates to a fault detection system for detecting a faulty temperature sensor in motor vehicles having an internal-combustion engine and at least one electronic control unit, which includes devices for detecting the downtime between the switching-off and the new start of the internal-combustion engine.
A fault detection system of the above-mentioned type is known, for example, from European Patent document EP 1 273 781 A2. In this case, only the temperature signal is taken into account, which signal is supplied by the temperature sensor to be diagnosed.
It is an object of the invention to improve upon a fault detection system of the above-mentioned type, on the one hand, with respect to its precision and, on the other hand, with respect to its simplicity as well as with respect to its accuracy, i.e., its exclusion of an incorrect fault detection.
This problem is solved by providing a fault detection system and method for detecting a faulty temperature sensor in motor vehicles having an internal-combustion engine and at least one electronic control unit, which includes devices for detecting the downtime between the switching-off and the new start of the internal-combustion engine. After a new start of the internal-combustion engine, an ambient-air temperature value determined by an ambient-air temperature sensor is compared in the electronic control unit with a coolant temperature value determined by at least one coolant temperature sensor if the detected downtime before the new start of the internal-combustion engine was greater than a defined minimum time value. A fault of the ambient-air temperature sensor is detected if the difference between the coolant temperature value and the ambient-air temperature value, at least with respect to the amount, is greater than a defined threshold value.
According to the invention, in the case of a fault detection system for detecting a faulty temperature sensor in motor vehicles having an internal-combustion engine and having at least one electronic control unit, which has devices for detecting the downtime between the switching-off and the new start of the internal-combustion engine, after a new start of the internal-combustion engine, an ambient-air temperature value determined by an ambient-air temperature sensor is compared in the electronic unit with a coolant temperature value determined by a coolant temperature sensor if the detected downtime before the new start of the internal-combustion engine was greater than a defined minimum time value. A fault of the ambient-air temperature sensor is detected if the difference between the coolant temperature value and the ambient-air temperature value, at least with respect to the amount, is greater than a defined threshold value.
The invention is based on the recognition that an easy diagnosis may be achieved by performing plausibility monitoring of temperature values of different temperature sensors which, however, have to be in a defined relationship to one another under certain operating conditions. As a result, complicated temperature models, which are normally used for diagnostic purposes involving temperature sensors, will not be necessary.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.